Studies of equilibrium, structure, and dynamics in the aqueous Al(iii)-oxalate-fluoride system by potentiometry, 13C and 19F NMR spectroscopy
The AlOx 1–3 (Ox = oxalate) species were identified in 0.6 M aqueous NaCl by 13C nuclear magnetic resonance (NMR). Rate constants and activation parameters for intramolecular cis/ trans isomerization of the Werner-type AlOx 2 − complex (k(298 K) = 5 s −1, ΔH # = 67 ± 5 kJ mol −1, ΔS # = −6 ± 6 J mol...
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| Published in: | Geochimica et cosmochimica acta Vol. 67; no. 15; pp. 2793 - 2803 |
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| Main Authors: | , , , , |
| Format: | Journal Article |
| Language: | English |
| Published: |
Elsevier Ltd
01-08-2003
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| Online Access: | Get full text |
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| Summary: | The AlOx
1–3 (Ox = oxalate) species were identified in 0.6 M aqueous NaCl by
13C nuclear magnetic resonance (NMR). Rate constants and activation parameters for intramolecular
cis/
trans isomerization of the Werner-type AlOx
2
− complex (k(298 K) = 5 s
−1, ΔH
# = 67 ± 5 kJ mol
−1, ΔS
# = −6 ± 6 J mol
−1 K
−1, the rate determining step could be the breaking of the Al–O(C=O) bond) and a very slow intermolecular ligand exchange reaction of AlOx
3
3− complex and the free ligand (
k
30(298 K) = 6.6 · 10
−5 s
−1, ΔH
# = 164 ± 17 kJ mol
−1, ΔS
# = 225 ± 51 J mol
−1 K
−1, D/I
d mechanism) were determined by dynamic 1D and 2D
13C NMR measurements. Mixed complexes, AlFOx, AlFOx
2
2–, AlF
2Ox
−, and AlF
2Ox
2
3–, with overall stability (logβ) of 11.53 ± 0.03, 15.67 ± 0.03, 15.74 ± 0.02, and 19.10 ± 0.04 were measured by potentiometry using pH- and fluoride-selective electrodes and confirmed by
13C and
19F NMR. The role of these complexes in gibbsite dissolution was modeled. The mixed Al(III)-Ox
2–-F
− complexes have to be considered as the chemical speciation of Al(III) in natural waters is discussed. |
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| ISSN: | 0016-7037 1872-9533 |
| DOI: | 10.1016/S0016-7037(03)00099-1 |